The documentation for this function states:

The FromStringToDate function converts a string to a Date_t using the relevant string format. The resulting date must be representable within the Gregorian calendar after the year 1600.

In reality, there is no check on the parsed value to ensure that the result is a correct Gregorian date. If this is important, callers should pass the result to the Std.Date.IsValidGregorianDate() function to determine validity.